7.99 is insane. If I were you I would keep paying on your current car to build your credit for a few more years. For an example, a 25K loan at 7.99 is $510 a month for 5 years. A 3.5% loan with the same terms is 450. That is $3600 you are giving to the bank in exchange for nothing.

Another way to build your credit is to open a credit card with a small limit, 1-$5,000. Make small purchases and pay it off in full every month. Dont put anything on the card you dont have the money for. These 2 things will build your credit pretty quick. Be sure to stay only about 25-30% maxed on your card. For example, if it is a $1000 limit never go above $300, and be sure to pay it every month so you dont pay interest.